Submarine sound-signaling device



Dec. 14 1926.

W. HAHNEMANN ET AL SUBMARINE SOUND SIGNALING DEVICE Filed Jan. 6, 1921Patented Dec. M, 1926.

WALTER HAENEMANN, F KITZEBERG, NEAR KIEL, AND HEINRICH HECHT, 0F KIEL,GERMANY, ASSIGNORS TO THE FIRM SIGNAL GESELLSCHAFT M. B. H., 0F KIEL,

GERM.

SUBMARHWE SOUND-SIGNALING DEVICE.

Application filed January 6, 1921, Serial No. 435,505, and in GermanyFebruary 29, 1916.

(GRANTED UNDER THE PROVISIONS OF THE ACT OF MARCH 3, 1921, 41 STAT. L,1313.)

This invention relates in general to submarine sound signaling devices,and more particularly to means in such devices for adjusting themagnitudes determined bythe vibrations set up in the sameand forestablishing definite relationships between parts of different or equaltuning.

By the present invention a means is provided by which, while maintaininga proper ratio of transformation of the amplitudes of motion of thevibrations during the transfer of the vibrations between the sender orreceiver proper and the sound propagating medium, the other factors ormagnitudes 1 that govern the character of the oscillations of thecomplete apparatus, such as the damping efi'ect and tuning, can be nradeto assume a desired value. The invention has to do with signalingapparatus comprising two or more bodies or structures each capable ofexecuting oscillations and all coupled together acoustically, one ofthese structures preferably acting chiefly as a sound radiating body,while another serves as an exciting or receiving member. An importantfeature of the invention consists in effecting such a close acousticcoupling of the vibratory structures that they allect each other in aconsiderable degree.

The term acoustic coupling has been selected to express the relationbetween the vibratory structures or units. The word coupling'is used inan analogous sense in the wireless telephone art, where primary andsecondary circuits are said to be closely or loosely coupled dependingupon the degree of influence which one exerts upon the other, or on theamount of energy transferred from one to the other.

The structures to be coupled belong, as a rule, to two fundamentallydifferent groups. lhe one group comprises the structures or bodies whichperform the function of radiating the sound waves into the propagatingmedium (for example, water), or which take in the sound waves from; thismedium (i. e. the radiators), while the other group embodies specialvibratory structures whose functions can be performed by detectors,microphones, electromagnets, etc., of a kind that comprises elasticmembers. When coupling such structures due consideration must be givento the fact that a certain amount of the mass or weight and of theelastic force of each structureoperates to structures; but, in addition,their natural rates of vibration must be made approximately or preciselyequal.

An obvious embodiment of the invention would be to make the fundamentalfrequencies of each of the two structures equal.

If this course is adopted where one of the vibratory structures is adiaphragma'outting against the water it will only be possible to operatewith relatively low rates of vibration; since, as the frequencyincreases, the diaphragm becomes thicker, and its mass greater, andhence the dam ing of the entire apparatus decreases. As Wlll be pointedout hereinafter a diaphragm having relatively large individual dampingis desired, to balance oil the relatively small individual dampinggenerally possessed by the other vibratory structure or strubturescoupled thereto.

But instead of utilizing the fundamental rate of vibration of one of thevibratory structures, say the sound radiating diaphragm, for couplingpurposes, it is possible to couple with a harmonic thereof. That is tosay, the vibratory structure which (for example) is to cooperate withthe diaphragm may be so tuned that its frequency or rate of vibration isequal or approximately equal to that of a harmonic of the diaphragm. Anadvantageous rate of vibration to use is one whereby the oscillationsexecuted by the diaphragm take the. form of alternating rises anddepressions, or outward and inward bulgings, of an annular zone lyingbetween the center and the periphery. 'lhat is to say, instead of thediaphragm being caused to execute a simple bulge first in the onedirection and then in the other, whereby the greatest travel isperformed by its centre and the travel executed by its other parts growssmaller as their distance -from the centre increases, the great- 1 esttravel or amplitude of motion may be caused to be executed by points ofthe diaphragm lying in a circular zone between the center and theperiphery. For the sake of brevity these oscillations of an annularportion of diaphragm will be referred to as ring vibrations of the same.As the fundamental rate of vibration of a diaphragm remains low when, inaccordance with this invention, the ring vibrations are employed, itsthickness is less than that of a diaphragm having a fundamental rate ofvibration as high as that of the utilized harmonic of the thinner plate.Hence, onaccount of the smaller mass of the parts of maximum travel, agreater damiping effect is obtained when the ring vibrations are used.

A feature of the invention, therefore,consists in using a radiator ordiaphragm that is of uniform thickness throughout and whose area andthickness are such that it has a fundamental rate of vibration that isso low compared with that of the vibratory structure coupled to it, thatthe rate of;vibration of this last-named vibratory structure is onlyapproached or equalled by the natural periodic time of the ringvibration or harmonic of the diaphragm. A result accomplished by thismeasure is that as far as the fundamental vibration of the radiator isconcerned no mutual acoustic interaction and hence no acoustic couplingbetween the special vibratory structure and the radiator takes place;whereas on account of the proximity between, or the equality of, theperiodic time, of the ring vibration of the-radiator and of the specialvibratory structure, a

strong acoustic coupling effect between these two bodies or structuresis produced as far as the frequency or periodic time of the ringvibration of the radiator is concerned.

Two examples showing how the invention may be applied in practice willnowbe adduced.

If, for instance, a vibrator) structure with a small intrinsic dampingeffect has to be used to obtain the proper ratio of transformation ofthe amplitudes of motion ofthe vibrations, while-the apparatus'as awhole shall be considerably dumped, the preferred procedure according tothe invention will be to couple to the said vibratory structure aradiating body with a large damping effect so as to thus obtain thedesired total damping effect. It will then be possible to predeterminethe size of each of the two individual damping effects, that is, thedamping effect in each vibratory structure after coupling, this beingdone in accordance with the law that when unequally damped vibratorybodies or structures are acoustically coupled together the dampingbecomes equally distributed in each.

If a sound-producin r or receiving apparatus with a particularly highfrequency a of resonance is desired, the two vibratory structures (theradiator and the special vibratory structure) will, in accordance withthe invention, be acoustically coupled so closely that an apparatus withtwo frequencies of resonance will result, one of which will be very muchhigher and the other very much lower than either :of the 'two individualfrequencies of resonance of the individual structures. The closer thecoupling is made the more the higher of the two frequencies of resonancewill be shifted up, 'so that by this means thedesired particularly highfrequency of resonance can be obtained. This closeness of coupling maybe secured in two ways; one, by bringing the individual frequenciesotthe vibratory structures closer together, and another by distributingthe masses of the coupled structures so that the common mass becomessmaller than the others.

The invention will be elucidated by reference to the drawing in whichFig. 1 shows a sound signaling receiving apparatus in which theindividual structures that are to be regarded as being coupled to eachother are, (1) a sound collecting or radiating diaphragm, and (2) aspecial vibratory structure formed of two masses connected by springs,the latter structure carrying a microphone.

Fig. 2 shows, in two separate curves, the amplitudes at differentfrequencies of the vibrations executed by the individual vibratorystructures before coupling, and in a single curve the two frequencies ofresonance that result from coupling the two individual structures. a v

Fig. 3 is a n'io'dification of the apparatus represented in Fig. 1, thechief difference being that the latter apparatus is equipped with anelertromagnet and may be used both as a sound producer and as a soundreceiver, the second or special vibratory structure that is coupled tothe diaphragm operating either to produce or to receive sound waves.

I I I I Fig. 1 shows a receiving apparatus made up of two coupledvibratory bodies or structures; the one vibratory structure being thediaphragm 1 with its supporting or holding frame or border 5 formed fromthe same material and the mass '2 in its centre; and the other vibratorystructure consisting of the weights or masses 2 and 4 and the elasticmembers 3 the mass 2 thus being common to both structures. Attached tothe weight 4 1s a microphone 6.

Let it be assumed that the dampingin the vibratory structure 2, 3, 4 isvery small, which might for instance be due to the'fact that themicrophone cannot be made large enough to present an opposing forcegreat enough to sufiiciently damp the vibrations of small amplitude thatthe energy of vibration causes the, mass 2 of the structure to emmaexecute. In a case like this the diaphragm is made to have a largeradiation damping, which can be done by making or arranging it in suchmanner that it is forced to execute ring vibrations of .a kind that willresult in the middle part of the diaphragm carrying out motions that aresmaller than, and in phase with, the motions of the marginal partsnearer to the periphery of the chaphragm, or else much smaller motionsthat are out of phase with the motions of the marginal parts. Now if thefurther condition is fulfilled that the frequency of the ring vibrationsof the diaphragm and the individual frequency of the structure 2, 3, ido not greatly differ, one of the two new frequencies of resonance ofthe coupled system will be higher, and the other Wlll be lower, than thetwo original frequencies of resonance. By coupling closer or looser theproximity of the two resulting frequencies can be altered and the tuningof the finished signaling apparatus or system thus predetermined. v I

It has been found by experience that a specially simple arrangement touse for the radiating body or structure is that of the hereinbeforedescribed ring vibration of a diaphragm. To make the radiation dampinglarge it is only necessary to arrange the diaphragm in such a way thatthe volume pressed out by its marginal or annular portion into'the soundpropagating medium is large-especially in comparison to any volume thatmight be simultaneous pressed inward at the middle of the diaphragmandthat the mass of the vibrating annular portion is not too large. Thismay be accomplished, for example, with flat diaphragms by rigidlyattaching to the diaphragm a second vibratory structure having the samenatural rate of vibration as the ring vibrations of the'diaphragm andconsisting of separate masses connected by an elastic member or members,one of said masses being attached to the middle of the diaphragm, andthis mass being made small in comparison with the other mass or masses.

In Fig. 2, in which the abscissae represent frequencies and theordinates the acoustic effect, F8 indicates the individual frequency ofresonance of the special vibratory structure 2, 3, 4; FM denotes thefrequency of resonance of the ring vibration or harmonic of the diahragm used for the purpose of coupling, t a resonance curve of thefundamental vibrations of the diaphragm being omitted. When the twostructures are acoustically coupled a single apparatus or system isformed having a resonance curve such as that indicated by the solid orunbroken graph with two crests.- f8 and fm are the frequencies ofresonance after coupling and correspond to the frequencies Fe and Fmrespeetively.

Of course the relative positions of the frequencies of resonance of theradiator and the special vibratory structure could be just the reverse.

In Fig. 3 the two coupled devices of which the entire apparatus iscomposed comprise the casing 5 with the diaphragm 1 and the central mass2 on the one hand, and the mass 2 with the spring plate '2' and themagnet 4- on the other. It is necessary in certain cases in accordancewith thisv invention-especially inthe cases of receiving apparatusconsisting of two coupled structures (the radiator and the exciting orsound transferring inember)to make the acoustic coupling between thevarious vibratory structures 0t which the entire apparatus is composedso close that the higher of the two resulting frequencies of resonanceis twice as high as the lower of these two frequencies. If, in

apparatus having a mass '2 which is common to two structures, whichstructures are in turn each providedwith their own unrestralned orfreelyvibratory masses 521ml 4,

theicondition is fulfilled that the free-mass 5 of the one structure(the radiator) is large compared to the common mass 2 and the free mass4 of the second structure, the required closeness of the coupling willbe attained in a satisfactory degree by making the common ma'ss 2smaller than, or atthe most as large as the second free mass 4. ltnpractice the free mass 5 is therefore generally large in comparison withmasses 2 and 4.

Other advantages of the invention are the following: It has not beenpossible with the acoustic structures hitherto employedat least not inworking with tuned sound signaling systems-to use the same apparatus forsignaling at several different frequencies. To render this possible wasan acoustic problem in connection with submarine sound signaling thatwas extremely difficult I to solve, because, on account of the largeelastic forces that have to be applied, it was not possible to bringabout a change of tunlng in a simple manner. Besides, the apparatus arealways arranged in the water or at places that are ditiicult to get at,so that to alter their tuning after installation they would always haveto be detached and removed. But with the novel method proposed herein itis possible to so arrange the apparatus that it is ready to respond atany moment to any one of at least two, and under certain circumstancesof more, distinct tones. With apparatus of this kind it is onlynecessary, to change from one frequency to another where electricalenergy is employed, to alter the speed of revolution of 1 all couplingit would also be possible to obtain more than two frequencies ofresonance.

Instead of two vibratory structures a larger number such as three may beused, the third structure being interposedbetween and coupled to theradiating vibratory structure or diaphragm and the vibratory structurethat is associated with the sound receiver or exciter proper.

The term means for coupling, as used in the claims, isintended to refernot simply to the mechanical connection between the coupled vibratorystructures, but to this in combination with the tuning and mass,relations of the said structures.

lVe claim:

1. In a sound signaling apparatus, a plurality of vibratory structureseach individually tuned to a definite pitch, said structures beingprovided with means for coupling them together acoustically whereby the'resulting frequencies of resonance of the structures in the coupledsystem are considerably different from the original frequencies.

2. In a sound signaling ap aratus, a vibratory structure tuned 'toaefinite pitch,

and asecond vibratory structure tuned to the same pitch, said vibratorystructures being provided with means for coupling them togetheracoustically whereby one of the-resulting frequencies of resonance ofthe structures in the coupled system is twice as great as the other.

In a sound signaling apparatus, a pinrality of vibratory structures eachindividually tuned to a definite pitch and individually damped to adefinite degree, said structures being provided with means for couplingthem together acoustically whereby the resulting frequencies ofresonance and dampings of the structures in the coupled system areconsiderably different from the original frequencies and dampings.

4. In a sound signaling apparatus, a vibratory structure tuned to adefinite pitch and having relatively high damping, a second vibratorystructure tuned to a definite pitch and having relatively low damping,said structures being provided with means for coupling them togetheracoustically whereby the damping at the resulting fre-.

quency of resonance of the coupled system corresponding to the vibratorystructure of relatively low damping is increased, and the damping of theresulting frequency of resonance of the coupled system corresponding tothe vibratory structure of relatively high damping is decreased, to aconsiderable extent.

5. In a sound signaling apparatus, a vibratory structure tuned to adefinite pitch and having relatively high damping, a second vibratorystructure tuned to a definite pitch and having relativelylow damping,said structures being provided {with means for coupling them togetheracoustically whereby the damping magnitudes are caused to becomesubstantially equalized.

6. A device according to claim 4, in which the vibratory structure havinrelatively high damping is a sound radiating diaphragm having highradiation damping.

7. In a sound signaling apparatus, a plurality of vibratory .structureseach individually tuned to the same pitch, and provided with means forcoupling them together acoustically including having the effectivemasses thereof proportioned relatively to each other, whereby theresulting frequencies of resonance of the structures in the coupledsystem are considerably different from the original frequencies.

8. In a sound signaling apparatus, a sound radiating diaphragm, and avibratory structure coupled thereto tuned substantially to the frequencyof an upper harmonic of the diaphragm to cause the diaphragm to vibratein the latter frequency.

9. In a sound signaling apparatus, a sound radiating diaphragm havinghigh radiation damping, and a vibratory structure coupled thereto tunedsubstantially to the frequency of an upper harmonic of the diaphragm tocause the diaphragm to vibrate in the latter frequency, the vibratorystructure and the diaphragm being so related that a relative largeportion of the diaphragm vibrates in phase when it is executing the saidharmonic vibration.

In testimony'whereof we aflix our signatures.

' HEINRICH HECHT.

WALTER HAH'NEMANNL

